An observation (kernel 3.13.0-155 is broken WRT Java) and a Grub2 / Ubuntu question

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An observation (kernel 3.13.0-155 is broken WRT Java) and a Grub2 / Ubuntu question

Robert Heller
OK, I just did updates at the local library, where the machines (except the
server's bare metal) run Ubuntu 14.04 LTS.  The kernel update (3.13.0-155)
crashes (sort of) when you try to run a Java program (specificly the Arduino
IDE (1.8.5)).

My question is this: what is the "magic" to change the default kernel to boot?
With the grub2 configuration "magic" it is not a simple matter of changing one
line /boot/grub/grub.conf, but seems to require something far more arcane and
there does not seem to be a simple man page that explains this.  Sigh...

On the two laptops I did the "brute force" method of just purging
(uninstalling) the 3.13.0-155 kernel (I'll have to go back and do the hack to
prevent updating the kernel). The PXE booted machines were easier -- I just
manually changed the symlinks in the tftp boot directory.

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Re: An observation (kernel 3.13.0-155 is broken WRT Java) and a Grub2 / Ubuntu question

Oliver Grawert
hi,

Am Freitag, den 17.08.2018, 15:57 -0400 schrieb Robert Heller:
> OK, I just did updates at the local library, where the machines
> (except the 
> server's bare metal) run Ubuntu 14.04 LTS.  The kernel update
> (3.13.0-155) 
> crashes (sort of) when you try to run a Java program (specificly the
> Arduino 
> IDE (1.8.5))
i guess thats:

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1787127

ciao
        oli
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Re: An observation (kernel 3.13.0-155 is broken WRT Java) and a Grub2 / Ubuntu question

Oliver Grawert
In reply to this post by Robert Heller
hi,
Am Freitag, den 17.08.2018, 15:57 -0400 schrieb Robert Heller:

> My question is this: what is the "magic" to change the default kernel
> to boot? 
> With the grub2 configuration "magic" it is not a simple matter of
> changing one 
> line /boot/grub/grub.conf, but seems to require something far more
> arcane and 
> there does not seem to be a simple man page that explains
> this.  Sigh...

whoops, i meant to also answer this one ... 

hold the shift key during boot to get into the menu
select the former kernel and boot it (see the bottom of the screen for
instructions)

after booting, edit /etc/default/grub, change the value of
GRUB_DEFAULT= to the grub menu entry you want booted as default and run
"sudo update-grub" ... 

that should switch the default to to the entry you picked.

ciao
        oli
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Re: An observation (kernel 3.13.0-155 is broken WRT Java) and a Grub2 / Ubuntu question

Robert Heller
At Fri, 17 Aug 2018 22:17:07 +0200 "Ubuntu user technical support,  not for general discussions" <[hidden email]> wrote:

>
>
>
> hi,
> Am Freitag, den 17.08.2018, 15:57 -0400 schrieb Robert Heller:
> > 
> > My question is this: what is the "magic" to change the default kernel
> > to boot? 
> > With the grub2 configuration "magic" it is not a simple matter of
> > changing one 
> > line /boot/grub/grub.conf, but seems to require something far more
> > arcane and 
> > there does not seem to be a simple man page that explains
> > this.  Sigh...
>
> whoops, i meant to also answer this one ... 
>
> hold the shift key during boot to get into the menu
> select the former kernel and boot it (see the bottom of the screen for
> instructions)
Ah, so Ubuntu/grub2 no longer uses the "Any" key and specificly uses the
"Shift" key.  I guess that was why my Any key foo did not work...

>
> after booting, edit /etc/default/grub, change the value of
> GRUB_DEFAULT= to the grub menu entry you want booted as default and run
> "sudo update-grub" ... 
>
> that should switch the default to to the entry you picked.

I could not get this to work.  It seems that I either get the "Advanced Ubuntu
Options", which would again default to -155 (if I select 1) or memtest (if I
select 2).  The kernel I want is in a *submenu*.  Arg -- somebody is being
excessively clever.



>
> ciao
> oliContent-Description: This is a digitally signed message part
>
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> Version: GnuPG v2
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> FNAAmwWHR0fADa7AzAFQmQfLfF3WLxHf
> =9nHn
> -----END PGP SIGNATURE-----
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> MIME-Version: 1.0
>
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Re: An observation (kernel 3.13.0-155 is broken WRT Java) and a Grub2 / Ubuntu question

Colin Watson
In reply to this post by Robert Heller
On Fri, Aug 17, 2018 at 03:57:09PM -0400, Robert Heller wrote:
> My question is this: what is the "magic" to change the default kernel to boot?
> With the grub2 configuration "magic" it is not a simple matter of changing one
> line /boot/grub/grub.conf, but seems to require something far more arcane and
> there does not seem to be a simple man page that explains this.  Sigh...

grub-set-default(8)

(Regarding submenus, you can set the default entry to something in a
submenu by taking the menu entry titles at each level and separating
them with '>' characters, e.g. "Advanced options for Ubuntu>Ubuntu, with
Linux 3.13.0-155-generic".  This is documented in 'info grub -n
default'.)

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